Catalytic reforming of hydrocarbons



Patented June 16, 1953 CATALYTIC REFORMING OF HYDROCARBON S Charles V.Berger, Western Springs, and Vladimir Haensel, Hinsdale, Ill., assignorsto Universal Oil Products Company tion of Delaware No Drawing.

, Chicago, 111., a corpora- Application January 27, 1950, Serial No.140,944

7 Claims. (Cl. 196-50) 1 This application is a continuation-in-part ofour co-pending application Serial No. 94,498, filed May 20, 1949.-

This invention relates to the catalytic conversion of hydrocarbonfractions containing naphthenes and paraffins. It is more specificallycon- .cerned with a particular method of reforming straight rungasolines and naphthas in the presence of hydrogen and reformingcatalysts comprising platinum or palladium composited with a crackingcomponent.

Catalysts comprising platinum or palladium composited with a crackingcomponent are especially useful in the reforming of hydrocarbons.Hydrocracking and isomerization of paraffins and dehydrogenation ofnaphthenes are among the principal reactions that are promoted by thesecatalysts, which are capable of increasing the octane number of straightrun gasolines and naphthas to values that are substantially higher thanthose that ordinarily can be reached by thermal reforming. In addition,the yield-octane number relationships realized with these catalysts aremuch better than are the corresponding relationships obtained in thermalreforming and in most of the prior catalytic reforming processes.However, these catalysts possess the disadvantage that the activitythereof decreases relatively rapidly with use due chiefly to thedeposition of carbonaceous material thereon.

As the activity of the catalysts declines it is necessary to compensatetherefor if a product of constant quality is desired. In any givenplant,

the most direct and inexpensive method of compensating usually comprisesincreasing the reaction temperature. .However, when this is done, it hasbeen found that hydrocracking is promoted to a greater extent than isthe dehydrogenation reaction. Consequently the balance between thesereactions is destroyed and greater losses to light gases as well asgreater consumption of hydrogen is encountered because of the relativelygreater proportion of hydrocracking. In addition, the rate of fouling ofthe catalysts is increased at the higher temperatures.

We have inventeda method of controlling the relative amounts ofhydrocracking and dehydrogenation, and, in particular, we have inventeda method of suppressing the tendency toward increased hydrocracking asthe reaction temperature is increased.

In one embodiment ourinvention relates to an improvement in thereforming of a hydrocarbon fraction containing paraffins and naphthenesby subjecting the same to the action of the catalyst comprising acracking component and a metal selected from the group consisting ofplatinum and palladium. in the presence of hydrogen at reformingconditions, said improvement comprising controlling the degree ofhydrocracking by regulating the partial pressure of water in thereforming zone.

In a more specific embodiment our invention relates to a reformingprocess whichcomprises continuously contacting hydrogen and a normallyliquid hydrocarbon fraction containing paraffins and naphthenes andboiling below about 425 F. With a catalyst consisting essentially of acracking component and a metal selected from the group consisting ofplatinum and palladium, said cracking component comprising silica and atleast one other metal oxide, at a temperature of from about 600 to about1000 F. and a pressure greater than about 250 p. s. i. a., increasingthe reaction temperature at intervals to compensate for loss in catalystactivity and concurrently increasing the water content of the reactionmixture to maintain the amount of hydrocracking substantially constant.

Reforming catalysts comprising platinum or palladium and a crackingcomponent become deactivated relatively rapidly by deposition ofcarbonaceous material thereon, with the result that they must beregenerated frequently if they are to be used for economic periods oftime. We have discovered that the tendency toward fouling is due to thehigh cracking or hydrocracking activity of the catalysts. We havefurther found that by maintaining a finite partial pressure of water inthe reforming zone, the hydrocracking activity can be reduced with aconcomitant reduction in the catalyst fouling rate. By appropriatecontrol of the water vapor content of the reaction mixture, the foulingrate can be reduced to a point at which catalysts can be used for monthswithout regeneration. As a consequence, reforming plants employing suchcatalysts can be built without regeneration facilities, therebyeffecting great savings in initial investment. In addition, markedsavings in operating costs are made possible by the omission of theregeneration step. In summary, a principal advantage of our. process isthat it makes possible'the reforming of straight run gasolines and thelike with catalysts comprispalladium or platinum and a crackingcomponent in a nonregenerative type of process. 7

As hereinbefore mentioned, an especially useful embodiment of ourinvention comprises the use of water to suppress the tendency towardincreased hydrocracking as the reaction temperature is raised during thecourse of the reforming run employing a catalyst comprising platinum orpalladium and a cracking component. However, it has been observed thatthe hydrocracking activity occasionally increases, at least for a periodof time, even though the reaction temperature is maintained at aconstant value. The exact reason for the gain in activity is not known,but there are indications that the gain is due to dehydration of thecatalysts and/or to an increase in the impurity content of the samebrought about by absorption of .or reaction with impurities present inthe charging stock that promote hydrocracking. Both .of these changes inactivity efiect the selectivity of the catalyst in a manner such thatthe hydrocracking reaction is increased relative to naphthenedehydrogenation reactions. In such a case, water or a water-formingcompound may be added .to the reaction zone to again bring thehydrocracking and dehydrogenation reactions back into .bal-

ance.

In a broad apsect, our inventionrelatesto .the use of water, .orcompounds which liberate water under the conditions .of reaction, in thereforming of hydrocarbons to control the balance ,between the variousreactions promoted by the platinumor palladium-cracking component caalyst. The amount .of hydrocracking can be .substantially independentlyregulated .by water addition with little .efiect on the other reactionspromoted by the catalysts. Thus, the use of water .or equivalentcompounds permits greater flexibility catalyst composition with resultinbenefits in catalyst life and product quality.

.Another useful application for our invention .isin the production ofaromatics ,by the dehydrogenation of charge stocks consistingessentially of naphthenes using a catalyst .of the type hereindescribed. The water suppresses hydrocracking of the naphthenes and thusmakes possible major yields of .aromatics.

The use of water as .a hydrocracking suppressor is particularlyadvantageous in that the eifect of water usually is only temporary.Therefore, the amount of hydrocracking obtainedin reforming processesemploying the catalysts herein described not only can be decreased byadding 'more water .or water-forming compounds to the reaction mixture,but the degree of hydrocracking can be increased by diminishing theamount of water or water-forming compounds added .to the reactionmixture. There appears to be up permanent impairment or deactivation ofthe catalyst from the amounts of water normally used inpracticing ourinvention.

The hydrocarbon stocks that will be converted in accordance with ourprocess comprise hydrocarbon iractions containing naphthenes andparaffins. The preferred stocks are those consisting essentially ofnaphthenes and parafiins, although in .some cases aromatics and/ orolefins also may be present. This preferred class includes straight rungasolines, natural gasolines, and the like. On the other hand, itfrequently is advantageous to charge thermally cracked gasolines orhigher boiling fractions thereof to our reforming P ocess. The gasolinemay be full boiling range gasoline having an initial boiling point offrom about 50 to about 100 .F. and an end boiling point within the rangeof .from about 325 to about 425 F. or itmay bea selected fractionthereof which usually will be a high boiling fraction, commonly referredto as naphtha, and generally having an initial boiling point within 4the range of from about to about 250 F. and an end boiling point withinthe range of from about 350 F. to about 425 F.

The catalysts comprising platinum, palladium, or other members of groupVIII of the periodic table having an atomic "weight greater than 100,and a cracking component that are preferred for use in our hydrocarbonreforming process may contain substantial amounts of platinum,palladium, etc., but, for economic as well as for prodnot yield andquality reasons, the platinum 01' palladium content usually will bewithin the range ;of from about 0.05% to about 1.5%.

The cracking component to be composited with the group VIII metal maycomprise any suitable cracking catalyst, either naturally occuring orsynthetically produced. Naturally occuring cracking catalysts includevarious aluminum silicates, particularly when acid treated to increaseactivity, such as Super-Filtrol, etc. Synthetically produced crackingcatalysts include silica-alumina, silica-zirconia,silica-aluminazirconia, silica-magnesia, silica-alumina-mag nesia,silica-alumina-thoria, alumina-boria, etc. These catalysts may be madein any suitable manner including separate, successive, or come-.cipitation methods of manufacture. Preferred cracking catalystscomprise silica-alumina or silica-.alumina-zirconia which preferably aremanufactured by commingling an acid, such as hydrochloric acid, sulfuricacid, etc., with com- .mercial water glass under conditions toprecipitate silica, washing with 'acidulated water or otherwise toremove sodium ions, commingling with an aluminum salt such as aluminumchloride, aluminum sulfate, aluminum nitrate, and/ or a zirconium salt,etc and either adding a basic precipitant, such as ammonium hydroxide,:to

precipitate alumina and/0r zirconia, or forming the desired oxide oroxides by thermal decomposition of the salt as the case may permit. Thesilica-alumina-zirconia catalyst may be formed by adding the aluminaand/or ziroonia salts together or separately. The catalyst may be in theform of granules of irregular size .and shape or the ground granules maybe formed into pellets of uniform size and shape by pilling, extrusion,or other suitable methods.

A particularly satisfactory method of forming a cracking component is toadd the acid to commercial water glass at a pH controlled to formsilicahydrogel, discharging the mixture of acid and water glass from arotating disc or nozzle into a bath of oil of sufficient depth so thatthe silicahydrogel sets into firm spheres during passage through the oilbath. The spheres may be removed from the bath in a suitable manner,such asby being transported in a stream of water disposed beneath theoil layer. The silica spheres may then be treated in any suitable mannerto remove sodium ions, followed by impregnation with a solution ofsoluble metal salt or salts. In another embodiment Silica-aluminaspheres, silica-magnesia spheres, etc. may be formed by coprecipitationmethods in a similar system.

It is preferred that the cracking component be driedat atemperature ofat least about 350 F. before the platinum or palladium is compositedtherewith. The cracking component may be dried at a temperature of fromabout 350 to about 500 F., and/ or calcined at a temperature of fromabout 500 to about 1400" .F. .or more prior to admixing the platinum orpalladium therewith.

-The platinum or palladium preferably is added to the dry crackingcomponent in the presence of ammonium hydroxide. A particularlypreferred methodof incorporating platinum with dry cracking. componentsis to ,commingle chloroplatinic acid with ammonium hydroxide to form amixture having a pH within the range of from about 5 to about andpreferably from about 8 to about 10 and then commingling this mixturewith the preformed particles. It is to be understood that the ammoniumhydroxide-platinum compound may be added first to the preformedparticles and that thereafter the other components may be added, andalso that these components may be composited either as cold or as hotsolutions.

Another method of impregnating the cracking component with platinum isto form a separate solution of chloroplatinic acid and hydrogen sulfidefollowed by impregnation of the cracking component with the resultingmixture;

After the platinum or palladium has been composited with the crackingcomponent, the resulting material is washed, dried, and calcined. Dryingordinarily will be effected at a temperature of from about 220 to 500 F.and calcination ordinarily will be carried out at a temperature of fromabout 500 to about 1000 F.

In the operation of our process, water or steam may be added in therequired amounts to the charging stocks or may be added directly to thereaction zone. If desired, materials that form water under theconditions prevailing in the reforming zone may be used in place ofwater. Materials of this type include oxygen and certain alcohols suchas tertiary butyl alcohol, peroxide, hydroperoxide, phenols, and carbonoxides, particularly carbon dioxide. In general, we prefer to use waterbecause of its low cost and because the use thereof does not introducecontaminating organic radicals into the reaction mixture. In order toachieve accurate control, it frequently is desirable to prefractionatethe hydrocarbon charging stock to remove dissolved water, oxygen, andoxygenated compounds therefrom and thereafter to add to the fractionatedcharge stock the desired amount of water or equivalent compound. If thisprocedure is followed, the partial pressure of water in the reactionzone can be closely regulated, since it is not influenced by variableamounts of water and the like in the charging stock. Instead of dryingthe charging stock by fractionation, it might be desirable in some casesto accomplish the same results by passing the charging stock at anelevated temperature through a bed of activated alumina or similardesiccant.

Hydrocarbons may be reformed in accordance with our process usingfluidized, fluidized-fixed bed, suspensoid, and moving bed types ofproc-* esses. However, we prefer to use fixed bed processes, primarilybecause processes of this type tend to minimize attrition losses of therelatively expensive catalysts. One fixed bed method of utilizing ourinvention comprises preheating hydrogen and hydrocarbon charge stocks toa conversion temperature, and passing the same in admixture with therequisite amount of water vapor through a plurality of substantiallyadiabatic reaction zones containing a catalyst comprising platinum orpalladium and a cracking component. In all but the last stages, thereaction is endothermic, hence the reactant streams passing between thereaction zones are reheated to the desired temperature. The reformedhydrocarbons are recovered, and the hydrogen is separated and recycledto the reaction zone. Another type of fixed bed process that isparticularly suitable for certain types of operations com- 6 prisespassing the hydrocarbon charging. stock together with hydrogen and therequisite amount of water through tubes containing catalyst, said tubesbeing subjected to radiant heat from a radiant flame and the resultinghot products of combustion. Here again the reformate is recovered andthe hydrogen is separated and re-; cycled to the reaction zone.

Hydrocarbon reforming operations carried out in accordance with ourinvention ordinarily will be conducted at temperatures of from about 600F. to about 1000 F. At temperatures in the vi-- cinity of 600 F. andlower, the aromatic-naphthene equilibrium is unfavorable, the reactionrates are quite low, and very low space velocities must be employed toobtain appreciable conversion. At temperatures in excess of 1000 F. asignificant amount of thermal reaction takes place accompanied by poorerliquid recovery and more rapid catalyst deactivation.

The pressures at which our process will be con-' ductedwill lie withinthe range of from about 5.0 to 1200 pounds per square inch; a totalpressure of at least 250 pounds ordinarilyis preferred. The weighthourly space velocity, which is defined as the weight of hydrocarbonscharged per hour per weight of catalyst in the reaction zone, should liewithin the range of from about 0.2 to about 40. The amount of hydrogencharged along with the hydrocarbons usually will be from about 0.5 toabout 15 mols per mol of hydrocarbon. I

The amount of water required to obtain the desired degree ofhydrocracking suppression can be determined by simple experimentation.For. example, it is possible to ascertain whether the amount of waterbeing added to the charging stock in a multiple adiabatic reactor systemis correct by observing the total temperature drop through the reactors.For example, if a fresh catalyst is giving a satisfactory productdistribution at a given total A T, then the amount of water added as therun progresses and the reaction temperature is increased should be suchas to hold the total A T essentially constant. If this procedure isfollowed the ratio between hydrocracking and aromatization will be heldsubstantially constant and, consequently, the product distribution willremain approximately the same as that experienced early in the run.However, if a substantial change in heat capacity of the material in thereaction zone has taken place by means such as a variation in the ratioor the composition of the recycle gas, this fact should be taken intoaccount. In such a case, a more accurate procedure would be to keep theproduct of heat capacity and A T substantially constant in order thatthe ratio between hydrocracking and aromatization be maintainedsubstantially constant.

A relatively simple method of determining the correct amount of water isto observe the composition of the reformate, particularly the degreeweeks and even months of operation without re- 7 amounts; of. thehydrocarbon reactions that are obtained.

We claim as our invention:

L In a reforming process wherein a normally liquid hydrocarbon fractioncontaining paraffins and naphthenes boiling below about 425 F. is passedwith hydrogen and at reforming conditions through a catalyst comprisinga metal selected from the group consisting of platinum and palladium anda composite of silica with at least one metal oxide selected from thegroup consisting of alumina, zirconia, magnesia and thoria to efiecthydrocracking of paraffins and dehydrogenation of naphthenes, andwherein the extent of said hydrocracking tends to increase in the laterstages of the processing period, the method of maintaining the extent of'hydrocracking substantially constant over said processing period whichcomprises introducing H20 to the reforming zone during the later stages,at least, of the processing period and regulating its partial pressureto suppress said increased tendency toward hydrocracking.

2 ..In a reforming process wherein a normally liquid hydrocarbonfraction containing parailms and naphthenes boiling below about 425 F;is passed with hydrogen and at reforming conditionsthrough a catalystcomprising a metal se lected from, the group consisting of platinum andpalladium and a composite of silica with at least one metal oxideselected from the group consisting of alumina, zirconia, magnesia andthoria to efiect hydrocracking of paraffins and dehydrogenation ofnaphthenes; and wherein the extent of said hydrocrackingtends toincrease with increasing temperature and decreasing catalyst activity,the method of maintaining the extent of hydrocracking substantiallyconstant over an extended time interval, including the period of reducedcatalyst activity, which comprises introducing H2O to the reforming zoneduring said period of reduced catalyst activity and regulating itspartial pressure to suppress said increased tendency towardhydrocracking. V

-3. In a reforming process wherein a normally liquid hydrocarbonfraction containing parafiins and naphthenes boiling below about 425 F.is passed with hydrogen and at reforming conditions through a catalystcomprising a metal selected from the group consisting of platinum andpalladium and a composite of silica with at least one metal oxideselected from the group consisting of alumina, zirconia, magnesia andthoria to effect hydrocracking of parafiins and dehydrogeneration ofnaphthenes, and wherein the activ ity of the catalyst declines withcontinued passage of the hydrocarbons therethrough, the method whichcomprises increasing the reforming temperature at intervals tocompensate'for reduced catalyst activity, whereby the extent of saidhydrocracking tends to increase, and increasing the water content of thereaction mixture with increasing temperature to suppress said increasedtendency toward hydrocracking.

4. The process of claim 1 further characterized in that the initialstages of said processing period are performed in the absence of addedwater and in that water is added to said hydrocarbon fraction duringsaid later stages.

5. The process of claim 2 further characterized in that the reforming iseffected in the absence of added water prior to said period of reducedcatalyst activity.

6. The process of claim 1 further characterized in that said H2O isintroduced to the reforming zone in the form of water in admixture withthe hydrocarbon fraction to be reformed.

7. The process of claim 1 further characterized in that said H2O isformed in situ in the reforming zone from a compound which liberateswater under the reforming conditions.

CHARLES V. BERGER. VLADIMIR HAENSEL.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,045,794 Pier June 30, 1936 2,398,674 Schulze Apr. 16, 19462,433,603 Danner et a1. Dec. 30, 1947 2,478,916 Haensel et al. Aug. 16,19.49.-

1. IN A REFORMING PROCESS WHEREIN A NORMALLY LIQUID HYDROCARBON FRACTIONCONTAINING PARAFFINS AND NAPHTHENES BOILING BELOW ABOUT 425* F. ISPASSED WITH HYDROGEN AND AT REFORMING CONDITIONS THROUGH A CATALYSTCOMPRISING A METAL SELECTED FROM THE GROUP CONSISTING OF PLATINUM ANDPALLADIUM AND A COMPOSITE OF SILICA WITH AT LEAST ONE METAL OXIDESELECTED FROM THE GROUP CONSISTING OF ALUMINA, ZIRCONIA, MAGNESIA ANDTHORIA TO EFFECT HYDROCRACKING OF PARAFFINS AND DEHYDROGENATION OFNAPHTHENES, AND WHEREIN THE EXTENT OF SAID HYDROCRACKING TENDS TOINCREASE IN THE LATER STAGES OF THE PROCESSING PERIOD, THE METHOD OFMAINTAINING THE EXTEND OF HYDROCRACKING SUBSTANTIALLY CONSTANT OVER SAIDPROCESSING PERIOD WHICH COMPRISES INTRODUCING H2O TO THE REFORMING ZONEDURING THE LATER STAGES, AT LEAST, OF THE PROCESSING PERIOD ANDREGULATING ITS PARTIAL PRESSURE TO SUPPRESS SAID INCREASED TENDENCYTOWARD HYDROCRACKING.